Device and method for heating of a seat

ABSTRACT

The invention is a device for heating a seat ( 3 ) comprising a heating element ( 2 ) connected to a control unit ( 1 ) which is arranged to feed a current (I) through the heating element ( 2 ), a detector unit ( 6 ) in connection to the heating element ( 2 ) connected to the control unit ( 1 ) with current (I) being fed when the measured temperature value falls below a predetermined desired value (T B ). The invention is characterized in that the detector unit ( 6 ) comprises at least one first temperature sensor ( 7 ) on or in the vicinity of the heating element ( 2 ) with at least one further temperature sensor ( 8 ) at a predetermined distance from the heating element ( 2 ). By means of the invention a more even heating of the seat is obtained with an increased comfort for a person sitting in the seat.

TECHNICAL FIELD

The present invention refers to a device for heating of a seat,comprising a heating element connected to a control unit which isarranged to feed a current through the heating element, a detector unitin connection to the heating element connected to the control unit, withcurrent being fed when a measured temperature value falls below apredetermined desired value.

The invention also relates to a method for heating a seat, comprising aheating element connected to a control unit which is arranged to feed acurrent through the heating element, which method comprises detectingthe current temperature in connection to the heating element andcontrolling the temperature by feeding said current through the heatingelement if said current temperature falls below a predetermined desiredtemperature.

The invention can in particular be applied in connection with heating ofelectrically heatable seats for those travelling in a vehicle.

STATE OF THE ART

Electrically heatable seats are used in contemporary vehicles forreasons of comfort and safety. Both the driver's seat and the otherseats in the vehicle can be arranged so that they can be heated by meansof special heating elements in the shape of electrically conductingwires, which are arranged in the shape of a heating coil in the seats.Such a heating coil is normally placed in the cushion and in thebackrest of the seats on production. In addition, the heating element isconnected to a current feeding unit which delivers current. In this way,the heating element can be heated to a suitable temperature.

A problem with previously known heating elements arises from a desire tohave a carefully adjusted temperature on the surface of each seat, i.e.on the surface which a person travelling in the vehicle will feel. Tothis end, the temperature of the heating element can be controlled bymeans of a temperature sensor which is arranged in close connection tothe heating element and which is connected to a central control unit. Bymeans of the temperature sensor and the control unit, the ambienttemperature can be detected. The control unit also comprises currentfeeding circuits which, for example, can be based on transistor or relaytechnology, for feeding current to the heating element. In this way, thecentral heating element is arranged to feed a certain current throughthe heating element until a certain desired value of the temperature isobtained. The setting of this desired value can, for example, be carriedout by means of fixed resistances or by means of an adjustablepotentiometer which is controlled by those travelling in the vehicle.

By means of the above described control method, current can be deliveredto the heating element until the central control unit indicates that thedesired value has been reached. When this is the case, the current feedis interrupted. This causes the heating element to successively becooled. When the heating element has cooled so much that its temperatureagain falls below the desired value, the current feeding to the heatingelement will be resumed. In this manner, the temperature control willcontinue as long as the system is active.

Although this previously known system normally provides a reliableheating and temperature control for a vehicle seat, it does, however,have certain drawbacks. Such a drawback arises from the fact thatprevious systems with a temperature sensor being arranged in doseconnection to or on the heating element give a relatively quick heatingof the sensor, which leads to the temperature control being startedbefore the surface temperature of the seat has reached the desiredvalue. In addition, relatively quick temperature shifts of the sensorare obtained during the temperature control. As a whole, this results inthe seat being heated relatively slowly, i.e. the seat is given atemperature which relatively slowly approaches the desired value. Thiscan be perceived by the user as a too slow heating of the seat. In orderto compensate this, a higher desired value of the temperature in theseat is often set. When the control is active during a longer period,the temperature in the seat approaches the too highly set desiredtemperature, which results in a too high temperature in the seat when itis used for a longer period of time.

In attempts to compensate for the above described problem, thetemperature sensor has been arranged at a distance from the heatingelement, which results in the temperature control being started afterthe surface temperature of the seat has reached the desired value. Thiscauses a temperature control of lower quality or no temperature controlat all, and also causes too high a temperature in the seat. Takentogether, this can be perceived as a too rapid heating with too largetemperature variations by somebody sitting in the seat. Placing thetemperature sensor far from the heating element also reduces thepossibility of discovering any possible short circuits in the heatingelement which can result in for example too high a temperature on thesurface of the seat.

In attempts to solve the said problems, there has traditionally been aneed for compromising when arranging the temperature sensor, with theresult that all of the said problems occur, although they are not asobvious as in the said extreme cases.

SUMMARY OF THE INVENTION

A primary purpose of the present invention is thus to provide improvedheating of a vehicle seat, in which the above described disadvantagesare eliminated, and which gives a surface temperature which during thecontrol will be more pleasant for a person sitting in the seat.

This purpose is obtained by means of a device of the initially mentionedkind, which is characterized in that the detector unit comprises atleast a first temperature sensor on or in the vicinity of the heatingelement, with at least one more temperature sensor at a predetermineddistance from the heating element.

The above purpose is also obtained by means of a method of the initiallymentioned kind, which is characterized in that it comprises detecting atemperature in the vicinity of the heating element and detectingadditionally one temperature at a predetermined distance from theheating element, which temperatures together give a value regarding thecurrent temperature to be compared with a desired temperature inconnection with said control.

The basic idea of the invention is that a temperature on or in thevicinity of the heating element and a temperature sensor at apredetermined distance from the heating element together will provideimproved control qualifies with smaller temperature swings and a surfacetemperature dose to the desired temperature. This in turn will lead toimproved comfort for somebody sitting in the seat.

Preferred embodiments will become apparent from the following dependentpatent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will in the following be described in connection to anexample of a preferred embodiment and the appended drawings in which

FIG. 1 is a principal circuit scheme which shows a device according tothe present invention,

FIG. 2 shows a control process according to prior art in more detail inthe case of only one temperature sensor being utilized placed close to aheating element,

FIG. 3 shows a control process according to prior art in the case ofonly one temperature sensor arranged at a relatively long distance froma heating element being utilized, and

FIG. 4 shows a control process according to the invention.

PREFERRED EMBODIMENT

FIG. 1 shows a principal circuit scheme of a device according to thepresent invention. According to the preferred embodiment, the inventionis intended to be used in connection with electrically heatable seats invehicles. A control unit 1 is shown in principle in the figure, theinternal components and connections of which are shown by means ofdashed lines. In the figure, all of the components of the control unit 1are not shown but only those parts which are necessary for theunderstanding of the invention.

The control unit 1 is arranged to feed a certain current I through aheating element 2. This heating element 2 is, as such, of a known kindand consists of an electrical conductor, which by means of itselectrical resistance forms a heating coil. The heating element 2 isarranged inside a vehicle seat, preferably in its cushion part 3, andconsists of heating wires, preferably in a pattern (see FIG. 1) which isintended to cover the main part of the surface of the cushion part 3. Inprinciple, the heating element 2 can also be arranged in the back restof the seat. Although FIG. 1 only shows one heating element 2, it ispossible to connect several such elements to the control unit 1, forexample in the shape of a separate heating element for the cushion ofthe seat 3 and a heating element for the back rest of the seat. In thecase where more than one heating element is used, these can be connectedto the control unit either in parallel or in series.

As shown in FIG. 1, the heating element 2 is connected to the controlunit 1 via two connections 4 and 5 respectively, of which saidconnection 5 also is connected to ground via for example a connection inthe body of the vehicle.

In connection to the heating element 2, there is arranged a detectorunit 6 which in turn comprises a first temperature sensor 7 and a secondtemperature sensor 8 which suitably are electrically connected to thecontrol unit 1 via the above-mentioned connection 5 and a furtherconnection 9. The temperature sensors 7, 8 preferably consist ofthermistors of the NTC type (“Negative Temperature Coefficient”) whichexhibit a temperature dependent resistance R₁ and R₂ which correspondsto the temperature T1 and T2 respectively, which through the positioningof the sensors 7, 8 are detected in connection to the heating element 2and at a predetermined distance from the heating element 2 respectively.The first temperature sensor 7 can be arranged directly on the heatingelement 2 or essentially adjacent to the heating element 2. The secondtemperature sensor 8 is arranged at a predetermined distance from theheating element 2, for example between two of the essentially parallellines which are defined by the S-shaped pattern in which the heatingelement 2 is positioned, or, depending on the shape of the seat 3, inanother position distant from the heating element 2 for example adjacentto the cushion surface. Normally, the second temperature sensor 8 thenhas a slightly lower temperature than the first temperature sensor 7,since the second sensor 8 is arranged farther from the heating element 2than the first sensor 7.

The detector unit 6 consists of the temperature sensors 7, 8 which arearranged together on the same flex board, i.e. a film-like supportingsubstrate shown in the figure by means of a rectangle with dashed lines.The flex board comprises a plurality of holes (not shown) which permitalternative positioning of the temperature sensors. The temperaturesensors 7, 8 are preferably coupled electrically in series, andconnected to the control unit 1 via leads coupled to the connections 4,9. According to an alterative solution, however, each of the temperaturesensors can be individually connected to the control unit. In the lattercase, there is a need for double inputs and measuring bridges in thecontrol unit. The detection by means of the temperature sensors 7 and 8will be described in detail below.

In addition there is a current source 10 connected to the control unit 1via a further connection 11. The current source 10 is preferably thestarting battery of the vehicle. The system additionally comprises anon/off switch 12, which is preferably integrated in the ignition lock ofthe vehicle (not shown). The switch 12 is connected to an additionalconnection 13 of the control unit 1. The control unit 1 is arranged sothat it can be activated, and thus afford heating of the heating element2 when the switch 12 is closed.

The control unit 1 comprises a logic part 14, which is preferablycomputer based, but which can also consist of known electronic circuits.The logic part 14 is connected to the above-mentioned connections 5, 9and 13 and is arranged to detect a temperature value T which correspondsto a composite value of the detected current temperature T1 and T2 ofthe temperature sensors 7 and 8 respectively.

With renewed reference to FIG. 1, it can be seen that the control unit 1comprises a switch unit 15 which depending on signals from the logicpart 14 feeds current I to the heating element 2.

The logic part 14 is thus arranged to obtain values of the localtemperature T1 and T2 of the temperature sensors 7 and 8 respectively,which corresponds to a resistance value of the respective temperaturesensor, and which together gives a combined resistance value whichconsists of the sum of the resistances of the two temperature sensorswhich gives a total resistance value which corresponds to the currenttemperature T. If the current temperature T falls below a predetermineddesired value T_(B), which in turn corresponds to a certain desiredtemperature T_(S) on the surface of the vehicle seat 3, the logic part14 will control the switch unit 15 to deliver current I to the heatingelement 2. When the desired value is reached the logic part 14 will cutoff the current feeding via the switch unit 15 to the heating element 2.

FIG. 2 shows a diagram which indicates the connection between thetemperature T and time. In the diagram, there is shown a first solidline 16 which in principle shows the process of a temperature controlaccording to prior art, in more detail a temperature control which usesone single temperature sensor which is arranged in close connection to(or even directly on) a heating element. The solid line 16 then showshow the temperature on the surface of the seat successively increasesfrom a low value and up to a certain set value T_(S). Furthermore, thesystem is arranged to heat the vehicle seat with a predetermined desiredtemperature value T_(B) which is compared to the temperature thatcorresponds to the signal from single temperature sensor. This desiredvalue T_(B) can in advance be set to a value which corresponds to thedesired temperature T_(S) on the surface of the seat, which can be forexample 35° C., and corresponds to the temperature on the surface of a“normal seat”, i.e. a kind of seat which has been defined in advancewith a certain given design, upholstery etc. or a value which is decidedby the user depending on his wishes.

It is previously known that systems with a single temperature sensorwhich is arranged in dose connection to or on the heating element willgive a relatively quick heating of the sensor, so the temperaturecontrol starts before the surface temperature of the seat has reachedthe desired value. In addition, relatively quick temperature shifts ofthe sensor are obtained during the temperature control. On a whole, thisresults in the seat being heated relatively slowly, i.e. the seat isgiven a temperature which relatively slowly approaches the desiredvalue. This process is indicated in FIG. 2 by means of a second solidline 17, which shows the supplied heat effect to the heating element,which in turn is an indication of how the temperature of the heatingelement varies depending on the switched on or off current feed throughthe heating element. Thus, the desired value T_(B) regarding thetemperature at which the current feed through the heating element isfirst switched off will be obtained relatively quickly, following whichrelatively quick on and off switching of the current through the heatingelement is carried out. Altogether, this results in the seat beingheated relatively slowly, i.e. it gets a temperature which relativelyslowly approaches the desired temperature T_(S). The user can perceivethis as a too slow heating of the seat.

It is also previously known that arranging one single temperature sensorat a long distance from the heating element will result in the oppositeof what has been described above, with a temperature control that startsafter the surface temperature of the seat has reached the desired value.This will result in a lower quality temperature control, or no controlat all, and also in a too high temperature in the seat. Altogether, thiscan be perceived as a too powerful and high heating with too largetemperature variations for the person sitting in the seat. The processis shown in FIG. 3, which similarly to FIG. 2 shows the connectionbetween the temperature T of the seat in question and time. In thefigure, there is shown with an additional solid line 18 a controlprocess in which this single temperature sensor is used, which then isplaced relatively far from the heating element. There is also shown withanother solid line 19 how heat effect is fed through the heating elementas a consequence of the said current feeding. From the figure, it can beseen that heating power is fed to the heating element during arelatively long time until a first switch-on takes place (i.e. at astate which corresponds to a certain desired temperature value T_(B) ofthe heating element). This means that the surface of the seat will beheated to a temperature which exceeds the desired value T_(S), which canbe perceived by the user as a too powerful heating of the seat.

With the above described traditional single temperature sensor, thepositioning of the sensor must be a compromise between the two casesdescribed above, which means that you either get a system with arelatively rapid temperature control and a too slow heating of the seat,or a system with a relatively slow temperature control and a processwith overshoot and a too powerful heating of the seat as a consequence.

Due to the above-mentioned problems of prior art, regarding for exampletoo large temperature variations when positioning a single temperaturesensor in close connection to a heating element, there is according tothe invention a measurement of the temperature in the vicinity of theheating element 2 and a further measurement at a predetermined distancefarther away from the heating element 2. This principle will now beexplained with reference to FIG. 4, which shows the connection betweenthe temperature T of the surface of the seat and time. The figure alsoindicates a desired value T_(S) regarding the temperature of the seat,which is decided by the user and a corresponding desired value T_(B) fora composite temperature of the two temperature sensors 7, 8 (see FIG.1).

Since the invention comprises a detector unit with two temperaturesensors 7, 8, a combined detected value is obtained, which consists ofthe sum of the resistances in question of the two temperature sensors.This total value then corresponds to a combined temperature value whichduring the heating of the seat is compared to a desired value T_(B)which in turn corresponds to the desired temperature T_(S) on thesurface of the seat. If the detected temperature exceeds the desiredvalue T_(B), the current feeding through the heating element will ceasein analogy to what has been described above. The combined resistancevalue of the temperature sensors 7, 8 will consist of two components, afirst component which is affected by the relatively quick temperaturechanges of the temperature sensor 7 which is arranged in close vicinityto the heating element 2, and a second component which is influenced bythe relatively slow temperature changes of the temperature sensor 8which is positioned relatively far from the heating element 2. Together,this gives a temperature control which corresponds to a balancingbetween the two mentioned known methods. Through proper tuning of thepositions of the temperature sensors 7, 8 according to the invention,there is then obtained an optimally adjusted heating of the seat, andthe desired temperature on the surface of the seat can be reachedrelatively quickly, however without the excessive temperature variationswhich follow the positioning of a single temperature sensor relativelyfar from the heating element. The too slow heating of the seat which isa result of positioning a single temperature sensor relatively close tothe heating element is not obtained either.

The control device according to the invention in this way will becomemore robust with regard to temperature variations, and will maintain itsspeed. A further advantage of the invention is that a combination of aquick and of a slow control process will result in a more “natural”perception by the person in the seat and in a raised level of comfort.

When the system is switched on and the temperature control is to, startthe logic part 14 (see FIG. 1) will control the switching unit 15 sothat the current I is fed to the heating element 2. It is here assumedthat the heating element 2 has a certain initial temperature when theheating starts. Since the current I flows through the heating element 2,its temperature will successively increase. The control of thetemperature of the heating element 2 will then be carried out dependingon whether a desired value T_(B) is reached. The present inventioncombines the two positions described above, with the two temperaturesensors 7 and 8 giving a combined resistance value which corresponds tothe current temperature T. The first temperature sensor 7 is positionedon or in the vicinity of the heating element 2, and the secondtemperature sensor 8 is positioned at a predetermined distance from theheating element 2 as has been described above. The temperature sensors7, 8 are preferably thermistors of the NTC type, i.e. “NegativeTemperature Coefficient” which means that the resistance of thethermistors decreases with increasing temperature. The two NTCtemperature sensors 7, 8 are connected either in series as shown in FIG.1, or in parallel depending on the desired control. As an alterative,the thermistors can also be of the PTC type, i.e. “Positive TemperatureCoefficient” which means that the resistance of the thermistorsincreases with increasing temperature. If the temperature sensors 7, 8are of the PTC type they are either connected in series or in parallel,depending on the desired control. The temperature sensors 7, 8 are fedwith current from the control unit 1, with the connected temperaturesensors detecting the local temperatures T1 and T2 and giving thecontrol unit 1 a combined value which reflects a current temperature T,which is a combined resistance value which corresponds to the twotemperatures and which is within the interval T1 to T2. The currenttemperature T in a better manner reflects the ambient temperature whichis to approach the desired temperature value. By means of saidarrangement, a reduction of the quick process given by the “warm” firsttemperature sensor 7 is obtained, as is also an increase of the slowprocess given by the “cold” second temperature sensor 8, which resultsin a process which is somewhere in between the two earlier described andwhich is illustrated in FIG. 4. The process will depend on, among otherthings, the position of the temperature sensors 7, 8 but will,regardless of this, give a better control of the surface temperature ina seat than known devices, which can be seen as advantageous andcomfortable by the person in the seat. An additional advantage of theinvention is that the control does not become as sensitive to theposition of the sensor as previously known devices, which leads toincreased position tolerances.

In conclusion, the invention is suitably utilized so that thetemperature sensor which is the coldest will control the process. Thiscan be utilized so that when starting to heat the seat, the secondtemperature sensor 8 is the coldest until it reaches the desired valueT_(B), at which point in time the heating element 2 is switched off,which means that the first temperature sensor 7 will cool off and willbecome the colder of the two temperature sensors 7, 8 and then it willbe the first temperature sensor 7 which controls the control process. Inthis way, the best properties of the two positions are combined, whichleads to a better control with a more stabile temperature around thedesired value.

The temperature sensors 7, 8 can have the same resistance and desiredvalue or different resistances and the same desired value, or the sameresistances but different desired values, depending on desires forspecific properties.

The temperature sensors 7, 8 can have the same thermic mass or differentthermic mass depending on requests for specific properties.

According to a further embodiment of the invention, a connection (notshown) is placed between the temperature sensors 7, 8, i.e. anelectrical connection which is coupled to the connection which connectsthe two sensors. The connection will be connected to the control unit 1,and used to provide information regarding the temperature sensors 7, 8.Such information can, for example, be used for diagnosing, or as ameasurement sensor for an algorithm for better control instead of, forexample, the average value of the two resistances.

The invention is not limited to that which has been described above,different embodiments are possible within the scope of the patentclaims. For example, the invention can in principle be used for heatingother seats than vehicle seats. Furthermore, various types oftemperature sensors can be used, for example thermistors with negativeor positive temperature coefficient. The temperature sensors 7, 8 do notneed to be arranged on a common flex board, but can be arranged asmultiple separate sensors.

A temperature sensor in the vehicle, for example for a climate controlsystem, can also in principle be used in combination with the invention.

Furthermore, the positioning of the temperature sensors can be differentdepending on the type of device which is to be heated and its material.For example, the “cold” sensor can be arranged on the surface of a seat3 if the seat is thick or between the threads of the heating element 2if the seat is thin.

The flex board with the two temperature sensors 7, 8 can be arranged inan arbitrary position for an arbitrary function. The flex board is notlimited to two sensors either but can comprise an arbitrary amount.

The invention is not limited to heating either but can also be used whencooling or ventilating the seat in question.

1. A device for heating a seat comprising: a heating element; a controlunit adapted to feed a current through said heating element; and adetector unit including at least a first temperature sensor juxtaposedwith said heating element within a first predetermined distance fromsaid heating element, and at least one additional temperature sensordisposed a second predetermined distance from said heating element, saidsecond predetermined distance being greater than said firstpredetermined distance, whereby said first temperature sensor and saidat least one additional temperature sensor are connected so that theyprovide a combined temperature value which is fed to said control unit,said current being fed through said heating element when said combinedtemperature value falls below a predetermined desired temperature value.2. The device according to claim 1, wherein said first temperaturesensor and said at least one additional temperature sensor are coupledin series.
 3. The device according to claim 1, wherein said firsttemperature sensor and said at least one additional temperature sensorare coupled in parallel.
 4. The device according to claim 1, whereinsaid first temperature sensor and said at least one additionaltemperature sensor are of the NTC type.
 5. The device according to claim1, wherein said first temperature sensor and said at least oneadditional temperature sensor are of the PTC type.
 6. The deviceaccording to claim 1, wherein said first temperature sensor and said atleast one additional temperature sensor have the same resistance and areworking towards the same desired value.
 7. The device according to claim1, wherein said first temperature sensor and said at least oneadditional temperature sensor have different resistances and are workingtowards the same desired value.
 8. The device according to claim 1,wherein said first temperature sensor and said at least one additionaltemperature sensor have the same resistance and are working towardsdifferent desired values.
 9. The device according to claim 1, whereinsaid first temperature sensor and said at least one additionaltemperature sensor have essentially the same thermic mass.
 10. Thedevice according to claim 1, wherein said first temperature sensor andsaid at least one additional temperature sensor have different thermicmasses.
 11. The device according to claim 1, whereby a connectionbetween said first temperature sensor and said at least one additionaltemperature sensor to provide information to said control unit.
 12. Amethod for heating a seat comprising: providing a seat including aheating element connected to a control unit which is arranged to feed acurrent through said heating element; detecting a first temperature bymeans of a first sensor disposed adjacent to said heating element withinfirst predetermined distance of said heating element, and detecting asecond temperature by means of a second sensor disposed a secondpredetermined distance from said heating element, said secondpredetermined distance being greater then said first predetermineddistance, said first and second temperature sensors being connected sothat they provide a common combined signal which defines a combinedtemperature value in the interval between said first and secondtemperatures depending on the positions of said temperature sensors;and, controlling said combined temperature by feeding said currentthrough said heating element when said combined temperature falls belowa predetermined desired temperature.